Hot Jupiter Planet May Induce 'Gravity Darkening' Of Own Sun To Cool Off, Astronomers Say

By Ken Croswell

What do you do if you're a hot Jupiter and want to cool off? Why, you use your gravity to lift up the surface of your sun, cooling it and creating a dark spot on the star.

In a forthcoming issue of The Astrophysical Journal Letters, astronomers will report using the Kepler spacecraft to observe the brightness of a star in the constellation Cygnus more than a million times.

Named HAT-P-7, this star has a hot Jupiter—a giant planet orbiting close-in (artist's conception shown)—which other scientists found before NASA launched the spacecraft.

The world's gravity raises the star's surface away from its hot center, causing part of the surface to cool by just a fraction of a degree Kelvin and produce a dark spot that lags behind the planet's position by a few hours.

If confirmed, this discovery is the first time astronomers have ever seen planet-induced "gravity darkening" and demonstrates Kepler's remarkable ability to detect even the subtlest of stellar signals.

ScienceNOW, the daily online news service of the journal Science